ROCKFORD — The sidewalk is crumbling and cracks line the pavement, but the Harrison Avenue bridge over the Rock River is still structurally sound, city engineers say.

Crews will repave the 37-year-old bridge’s surface early next year, part of a $1.5 million project that could give the bridge another 15 years of useful life.

It’s part of a balancing act played at City Hall, to maintain bridges long enough so the city can space out the major multi-million-dollar overhauls long enough to save and capture enough money to pay for them.

And with the multi-year project to replace the Morgan Street bridge nearing completion, city officials are looking to what’s next.

Bridge repairs, like road repairs, are a never-ending process, said Pat Zuroske, Rockford capital program manager.

“Basically, we decided to replace the deck on Harrison in order to buy 10 to 15 years, at which time we’ll have saved enough money to replace the bridge,” Zuroske said.

The Harrison Avenue crossing is one of 108 bridges in Rockford, and one of eight that crosses the Rock River.

They’re all ranked every other year by independent inspectors on a scale of zero to 100, with 100 being the most sufficient. A number of conditions factor into the ratings other than the structural condition of the bridge, including traffic, age, design, number of accidents and the importance to the traffic flow of the city.

Inspectors ranked the Harrison Avenue bridge a 54.8 in 2011, according to city records. The bridge’s 2013 inspection results will be released sometime in January, Zuroske said.

If a bridge sufficiency rating drops below 50, while it could still be considered structurally safe, it would also qualify for federal funding to be replaced. Even with federal funding, a new bridge costs millions of local taxpayer dollars.

The busier Jefferson Street bridge, given a 45.8 rating in 2011, will be the next city bridge to be replaced. It will be about a 10-year, $50 million project, with engineering and design set to start in 2014.

Local taxpayers will be on the hook for 20 percent of the construction cost, an estimated $10 million, and all design and land acquisition costs, Zuroske said.